Disclosed in the embodiments herein is an improved automatic self-diagnostics system for detecting operational anomalies and the like in the control system of an in situ color sensor. More specifically, particular diagnostics for a color spectrophotometer based system for color detection, calibration and/or correction which is highly suitable for incorporation into the color calibration or control system of various color printing systems or other on-line color control or color processing systems.
The diagnostics systems of the disclosed embodiments have different features or aspects. One is to insure correct interrogation of the operating characteristics of an in situ (on line) color sensor for sensing xerographically printed different color test patterns in a color printer. More specifically, to diagnostically provide assurance that the color sensor is reading the correct (intended) color test target patches and thus is operating to provide reliable color data collection. Especially, for measuring such color test targets on paper sheets moving at variable speeds.
More specifically, in one aspect of the diagnostics systems of the disclosed embodiments, in a diagnostics mode a series of diagnostic test patches are automatically generated, printed on test sheets and read by the spectrophotometer or colorimeter and its output signals are compared to acceptable signal levels, in order to assure that the spectrophotometer or colorimeter measurements represented thereby are correct. In particular, providing a series of test targets of different light absorption density for testing the sensed signal responses to the illumination of the different test targets to their illumination by the respective different LEDs or other light sources. That is, generating a series of solid area test patches of varying optical density, position, and/or colors, which are respectively illuminated and read by the light emitters and photodetectors of the spectrophotometer or calorimeter. Those readings are used to determine whether the device is operating correctly by comparing them to expected readings.
Another aspect of the disclosed diagnostics systems of the disclosed embodiments is to provide automatic confirmation testing for the density and readability of fiducial marks on the test sheets of multiple color test patches, which fiducial marks automatically control the reading of respective said color test patches by an associated spectrophotometer or calorimeter. That is, a periodic automatic diagnostics interrogation for malfunctions in a fiducial mark sensing system comprising xerographically produced fiducial marks and an optical fiducial mark sensor used to trigger the occurrence of a desired event, such as the arrival of a test pattern for measuring a color. This provides assurance that color measuring triggering system is robust enough for reliable color data collection.
In one embodiment thereof the spectrophotometer normally used for color patch color sensing is used in a diagnostics mode for testing the developability (printing) curve for the marking material of the color (usually black) used for the fiducial marks, by printing none, varying amounts, and normal amounts, of the fiducial marking material into what would normally be color test patch areas. That is, assuming the spectrophotometer tests normally, the spectrophotometer may be used, in effect, as a fiducial mark detector for the testing of the (separate) optical fiducial mark detector. As further disclosed in the embodiments, a diagnostic routine of having the fiducial mark detector and the spectrophotometer sensor(s), separately or at the same time, examine a series of automatically printed graded density test patches of the fiducial marking material, starting with the darkest, and counting them until they are no longer detectable, can indicate, inter alia, at which density level of the fiducial marking material on the test sheets the fiducial mark detector will fail to detect fiducial marks (fail to deliver control signals). This diagnostic test can also tell how close the fiducial mark detector is to failure to read normal density fiducial marks.
By way of background, the general concept of fiducial marks adjacent to, and identifying, respective test color patches, and optical fiducial mark detectors separate from (but electronically controlling) the spectrophotometer detector, are known (see the above-cited and other references). However, there are practical restraints, associated with the particular spectrophotometer, etc., on how many distinguishable test patches can be printed on a normal sheet size test sheet, that is, how small they can be and how closely they can be spaced. Also, if the spectrophotometer is fixed relative to a sheet path, and the test sheet is moving normally in one direction in that path, the area of the test sheet in which the test patches can be printed and still be xe2x80x9cseenxe2x80x9d by the spectrophotometer as the test sheet moves past the fixed position spectrophotometer may be further limited. Also, the movement velocity of the test sheet relative to the spectrophotometer may vary. Yet, more test patches per sheet means that fewer test sheets need be used, and thus is desirable. Furthermore, even the blackest toner may not print sufficiently black fiduciary marks on print media (the test sheets) to be reliably detected if the printer developablity level control is out of adjustment, the black toner supply is depleted, the fiducial mark optical sensor is contaminated with paper lint or toner, the sensor signal amplifiers drift, etc. Yet, accurately knowing which one of the many test patches on a test sheet the spectrophotometer is reading (i.e., which spectrophotometer output signals are for which test color or test gray shade) is vital, and a missed fiducial mark can confuse that. Using mere blank (unprinted white paper) spaces in between color patches read by the spectrophotometer itself as the fiducial indicators for counting reading discrete patches is known, but is not as reliable as separate dark fiducial marks read by a separate detector therefor.
Printing fiducial marks along side of, rather than in between, each color test patch is desirable, although not essential. It can enable closer spacing of the color test patches. Also, it can provide more mounting location lateral freedom or space for a separate fiducial mark optical sensor (detector) without interference with the spectrophotometer illuminator(s) and detector(s).
Further by way of background, there is an additional significant challenge in implementing a multiple (or plural) LED type of spectrophotometer color sensor in a reprographic machine paper path to read accurately in xe2x80x9creal time.xe2x80x9d That is, utilizing a type of spectrophotometer as shown in the example herein and as further exemplified and described in the above cross-referenced applications, in which each small test patch is sequentially illuminated by different LEDs of different illumination spectra, and the separate reflectances of those separate sequential illuminations of that same test patch are reliably detected, all while the test sheet bearing that and many other such test patches to be read is on normal print media rapidly passing by the spectrophotometer sensing zone in xe2x80x9creal time.xe2x80x9d As noted above, this xe2x80x9creal timexe2x80x9d reading accuracy is facilitated by using separate black fiducial or timing marks associated with each test patch, and a separate reflective sensor for those fiducial marks, which may be attached to the side of the multiple LED spectrophotometer. That fiducial mark sensor can be a simple commercially available optical sensor, such as from Vactec 130E01721, which, for example, can change its output signal state from low to high (e.g., xcx9c0.2V to 4.8V) when a black mark imprinted alongside a test patch passes within the illumination/sensing area of that fiducial mark sensor. That control signal can then control the operation of the spectrophotometer LEDs to read the test patches synchronous with the arrival and passage of the desired test patch in the sensing area of the spectrophotometer.
As disclosed in the embodiments, the spectrophotometer test patch sensor(s) and the associated fiducial marks sensor may be operating synchronously and in coordination. Both may be desirably located in a printer paper path, which can be an electrically noisy and easily optically contaminating area, such as from paper lint or loose toner. Thus, it is possible that malfunctions of that test patch reading equipment and process may occur which would cause test patch measurement errors.
Therefore it is desirable to be able to diagnostically interrogate and evaluate readings from the sensors with appropriate tests to assure proper operation prior to and/or in between regular print job printings and/or at other intervals during use. It is also desirable to be able to provide said diagnostic tests with minimal additional cost, without requiring additional hardware, substantially increased machine overhead or run time, and with relatively low paper and toner consumption.
It must be appreciated that some of the specific details of the exemplary diagnostics tests of the disclosed diagnostics systems embodiments may vary depending on the type of spectrophotometer being utilized. The spectrophotometer example shown here has only four different LEDs, all commonly central optical axis mounted, and four angularly and radially spaced multiple-photo-site three or four color detectors. In contrast, the earlier-filed above-cited incorporated applications, etc., show spectrophotometers with a single central optical axis sensor and a much larger number LEDs, and in which those LEDs are angularly and radially spaced from the central optical axis, i.e., reversed in position with the currently illustrated photodetectors. The subject diagnostics systems are suitable for either of those, and various other, spectrophotometers and color testing equipment.
Various of these diagnostics tests may also be usable for testing of some off-line spectrophotometer or other color testing systems, including those in which a spectrophotometer is not a part of a color printing system. Even if the spectrophotometer is moved relative to a stationary diagnostics test sheet, instead of being stationarily mounted in a color printer paper path. However, controlled relative movement may still be desirable.
With the disclosed diagnostics systems, by using relatively simple test sheets of different types, interrogation of various aspects the proper operation of spectrophotometer LEDs, spectrophotometer sensor(s) {photodetectors(s)}, and any separate fiducial marks sensor, can all be accomplished. The test sheets may be provided by automatically printing in the subject printer an appropriate set of test sheets with test patterns of selected or known density and patch locations printed on conventional available white paper print media, and conventionally feeding those test sheets through the sensing area (nip) of the spectrophotometer. The output signal responses of the sensor(s) may then be recorded and compared to the expected response for that respective test. Significant deviations from the expected signal outputs may be interpreted as malfunctions, and remedial actions may then be initiated, automatically or by diagnostic displays. For example, automatically initiating further diagnostic tests, and/or displaying an operator or tech rep instruction to clean, or replace, potentially contaminated or defective sensors or associated circuitry.
Of background interest as to a xe2x80x9cself calibrating color printerxe2x80x9d, and color print test patterns, is an HP U.S. Pat. No. 5,508,826 issued Apr. 16, 1996 to William J. Lloyd, et al.
Referring now to the spectrophotometer embodiment disclosed herein, as noted, it is merely exemplary. This particular example is disclosed in greater detail in the above-cited applications, especially said D/99660Q, now U.S. Pat. No. 6,351,308 issued Feb. 26, 2002 and Q1, now U.S. Pat. No. 6,538,770 issued Mar. 25, 2003, and need not be described in great detail herein. It may employ only a small limited number of different spectra LED or other illumination sources, as shown, or up to sixteen or more different illumination sources. Desirably it can provide multiple data outputs suitable for broad spectral data reconstruction from a single or plural different spectral responsive photo-sites, by detecting light reflected by a sequence of single or plural color test target areas sequentially illuminated by those illumination sources, and/or white light illuminated, to rapidly provide broad spectrum data
Although not limited thereto, the exemplary spectrophotometer of the embodiment herein is shown and described herein in desirable combination as an integral part of an automatic on-line continuous color table correction system of a color printer, in which this low cost spectrophotometer may be affordably provided in the output path of each color printer for automatic measurement of printed color test patches of printer output, without any manual effort or intervention being required. Such color control systems are further described in the above and below cited co-pending applications and patents. For example, in Xerox Corp. U.S. Pat. No. 6,178,007 B1, issued Jan. 23, 2001, based on U.S. application Ser. No. 08/786,010, filed Jan. 21, 1997 by Steven J. Harrington, now U.S. Pat. No. 6,178,007 issued Jan. 23, 2001, Attorney Docket No. D/96644, entitled xe2x80x9cMethod For Continuous Incremental Color Calibration For Color Document Output Terminals.xe2x80x9d The European patent application equivalent thereof was published by the European Patent Office on Jul. 22, 1998 as EPO Publication No. 0 854 638 A2. Also, Xerox Corp. U.S. Pat. No. 6,222,648, issued Apr. 24, 2001, based on U.S. application Ser. No. 08/787,524, also filed Jan. 21, 1997, by Barry Wolf, et al, entitled xe2x80x9cOn Line Compensation for Slow Drift of Color Fidelity in Document Output Terminals (DOT),xe2x80x9d now U.S. Pat. No. 6,222,648 issued Apr. 24, 2001, Attorney Docket No. D/96459. Also noted in this regard are Xerox Corp. U.S. Pat. No. 6,157,469, issued Dec. 5, 2000 and filed May 22, 1998 by Lingappa K. Mestha; Apple Computer, Inc. U.S. Pat. No. 5,881,209, issued Mar. 9, 1999; U.S. Pat. No. 5,612,902 issued Mar. 18, 1997 to Michael Stokes, and other patents and applications further noted below.
A low cost, relatively simple, spectrophotometer, as disclosed herein, is thus particularly (but not exclusively) highly desirable for such a xe2x80x9ccolorimetryxe2x80x9d function for such an on-line printer color correction system. Where at least one dedicated spectrophotometer is provided in each printer, its cost and other factors becomes much more significant, as compared to the high cost (and other unsuitability""s for on-line use) of typical laboratory spectrophotometers.
An early patent of interest as to using a calorimeter in the printed sheets output of a color printer is Xerox Corp. U.S. Pat. No. 5,748,221, issued May 5, 1998 to Vittorio Castelli, et al, filed Nov. 1, 1995 (D/95398). This patent is also of particular interest here for its Col. 6, lines 18 to 28, description of measuring color:
xe2x80x9c . . . by imaging a part of an illuminated color patch on three amorphous silicon detector elements after filtering with red, green and blue materials. The technology is akin to that of color input scanners. The detector outputs can be used as densitometric values to assure color consistency. Calibration of the resulting instrument outputs against measurement by laboratory colorimeters taken over a large sample of patches made by the toners of the printer of interest allows mapping to absolute color coordinates (such as L*a*b*).xe2x80x9d
Automatic on-line color recalibration systems can be much more effective with an on-line color measurement system where a spectrophotometer may be mounted in the paper path of the moving copy sheets in the printer, preferably in the output path after fusing or drying, without having to otherwise modify the printer, or interfere with or interrupt normal printing, or the movement of the printed sheets in said paper path, and yet provide accurate color measurements of test color patches printed on the moving sheets as they pass the spectrophotometer. That enables a complete closed loop color control of a printer.
Although the specific exemplary low cost color spectrophotometer embodiment herein is shown as a desirable on-line part of an exemplary color printer automatic color control system for color calibration and re-calibration, it will be appreciated that this or other versions of that spectrophotometer are not limited to that disclosed application. Color measurements, and/or the use of color measurements for various other color quality or consistency control functions, are also important for many other different technologies and applications, such as in the production of textiles, wallpaper, plastics, paint, inks, etc. Thus, the disclosed spectrophotometer and/or its related color detection system and/or controls may have applications in various such other fields where various other materials or objects are desirably color tested and/or process controlled. Another application of improved on-line color printing control enabled by a low cost, non-contact, spectrophotometer for spectral analysis and direct color control feedback is to provide much more accurate, yet low cost, local user digital printing of remotely transmitted (over the internet or otherwise) digital camera (or scanned optical camera) color photographs over the internet. Color control of printed photographs, especially flesh tones, is particularly customer sensitive. Plural color test patches can be automatically generated and transmitted with the original photographic image source (adjacent to, or on pages before, or after, the photographic image) for reading their color reproduction accuracy at the output of the remote printer as described herein or otherwise.
By way of general background, studies have demonstrated that humans are particularly sensitive to spatial color variations. Typical full color printing controls, as well as typical color controls in other commercial industries, still typically utilize manual off-line color testing and still often require relatively frequent manual color adjustments by skilled operators. Both the cost and the difficulty of on-line use of prior color measurement apparatus and control systems, and the need for manual recalibration steps, has heretofore inhibited automation of many of such various commercial color testing and color adjustment systems. The disclosed lower cost spectrophotometer addresses both of those concerns.
By way of some examples of the construction or design of various other color spectrophotometers themselves, besides Xerox Corp. U.S. Pat. No. 5,748,221 above, and, especially, the above cross-referenced U.S. application Ser. No. 09/535,007, filed Mar. 23, 2000 by Fred F. Hubble, III and Joel A. Kubby, there is noted HP U.S. Pat. No. 5,671,059, issued Sep. 23, 1997; and HP U.S. Pat. No. 5,272,518, issued Dec. 21, 1993; Accuracy Microsensor, Inc. U.S. Pat. No. 5,838,451 and U.S. Pat. No. 5,137,364, both issued to Cornelius J. McCarthy on Nov. 17, 1998 and Aug. 11, 1992, respectively; Color Savvy U.S. Pat. Nos. 6,147,761, 6,020,583, 5,963,333; BYK-Gardner U.S. Pat. No. 5,844,680; and Colorimeter U.S. Pat. No. 6,157,454.
Also of background interest here is that white (instead of narrow spectrum) LED illuminators and plural sensors with different color filters are disclosed in an EP Patent Application No. 0 921 381 A2, published Sep. 6, 1999 for a color sensor for inspecting color print on newspaper or other printed products.
By way of further background, or expressing it in other words, for a desirably low cost implementation of a spectrophotometer with plural light emitting diodes (LEDs) as the respective different color light sources, LEDs of different colors may be selected and switched on individually in sequence to illuminate a test target for a brief length of time sufficient for enough information to be extracted by a photocell of the reflectance spectra of the substrate. Over a number of years, a concentrated effort in the Xerox Corporation Wilson Research Center has designed and built a relatively low cost experimental spectrophotometer using, for example, 10 LEDs, as part of a printer color control system dynamically measuring the color of test patches on the printed output media xe2x80x9con line,xe2x80x9d that is, while the media is still in the sheet transport or paper path of a print engine, for real-time and fully automatic printer color correction applications. A limited example of that color control system capability was presented in a restricted public technology capability demonstration by Xerox Corporation at the international xe2x80x9cDrupa 2000xe2x80x9d show in Germany (without public disclosure of the hardware, software or technical details, or any offers to sell). Further details of the specific spectrophotometer embodiment so utilized are disclosed in the prior above first-paragraph cross-referenced patent application by Fred F. Hubble, III and Joel A. Kubby. Each LED thereof was selected to have a narrow band response curve in the spectral space. Ten LEDs provided 10 color calibration measurements on the spectral reflectance curve. The LEDs are switched on one at a time and the reflected light was detected by a single photodetector as a photo-current which may be integrated for few milliseconds to give a voltage output. Thus, 10 voltage outputs per each measured color test patch are available with such a spectrophotometer using 10 LEDs. These voltages may be converted directly to L*a*b* color space, or to 10 reflectance values and then to L*a*b* color space coordinates (if needed). The cost of that LED spectrophotometer hardware includes the head and printed wire board for mounting the LEDs, the lenses, the detector(s) and the basic switching electronics.
Other than the above Xerox Corp. experimental spectrophotometers, some others presently known include a grating-based spectrophotometer made by Ocean Optics Inc., LED based sensors marketed by xe2x80x9cColorSavvyxe2x80x9d and Accuracy Microsensor (such as in their above-cited patents); and other spectrophotometers by Gretag MacBeth (Viptronic), ExColor, and X-Rite (DTP41). However, those other spectrophotometers are believed to have significant cost, measurement time, target displacement induced errors, and/or other difficulties, for use in real-time printer on-line measurements.
The particular example of a spectrophotometer illustrated herein may utilize a component chip or portion of a low UMC commercially available color image sensor array or bar, such as imager bars mass produced for commercial use in document scanners, combined with a suitable (and reduced) number of LEDs or other light sources to provide a spectrophotometer of suitable speed and spectral outputs for even lower cost than the above-described low cost 10 LED spectrophotometer. However, the diagnostics systems disclosed herein are not limited to any such specific spectrophotometer.
As used in the patent claims and elsewhere herein, unless otherwise specifically indicated, the term xe2x80x9cspectrophotometerxe2x80x9d may encompass a spectrophotometer, colorimeter, and densitometer, as broadly defined herein. That is, the word xe2x80x9cspectrophotometerxe2x80x9d may be given the broadest possible definition and coverage in the claims herein, consistent with the rest of the claim. The definition or use of such above terms may vary or differ among various scientists and engineers. However, the following is an attempt to provide some simplified clarifications relating and distinguishing the respective terms xe2x80x9cspectrophotometer,xe2x80x9d xe2x80x9ccolorimeter,xe2x80x9d and xe2x80x9cdensitometer,xe2x80x9d as they may be used in the specific context of specification examples of providing components for an on-line color printer color correction system, but not necessarily as claim limitations.
A typical xe2x80x9cspectrophotometerxe2x80x9d measures the reflectance of an illuminated object of interest over many light wavelengths. Typical prior spectrophotometers in this context use 16 or 32 channels measuring from 400 nm to 700 nm or so, to cover the humanly visible color spectra or wavelength range. A typical spectrophotometer gives color information in terms of measured reflectances or transmittances of light, at the different wavelengths of light, from the test surface. (This is to measure more closely to what the human eye would see as a combined image of a broad white light spectra image reflectance, but the spectrophotometer desirably provides distinct electrical signals corresponding to the different levels of reflected light from the respective different illumination wavelength ranges or channels.) In other words, spectrophotometers may be considered as belong to the class of instruments known as reflectance densitometers. These devices measure the optical reflectivity of objects of interest, such as painted materials, fruit, printed media, etc., and operate by reflecting light off these objects onto a detector. Most other color densitometers known to the inventors are test devices typically employ broadband light sources such as tungsten filament lamps or flashed Xenon lamps plus means for determining the spectral content of the light reflected off the object. The latter is typically done with gratings or prisms which separate the light according to its wavelength in concert with an array of detectors disposed to collect flux of a particular wavelength, or, alternatively, a single detector that is mechanically scanned across this spread spectrum. Costs of these instruments typically range from $2,400 to $20,000, making them unsuitable for low cost installed applications.
A xe2x80x9ccolorimeterxe2x80x9d normally has three illumination channels, red, green and blue. That is, generally, a xe2x80x9ccolorimeterxe2x80x9d provides its three (red, green and blue or xe2x80x9cRGBxe2x80x9d) values as read by a light sensor or detector receiving reflected light from a color test surface sequentially illuminated with red, green and blue illuminators, such as three different color LEDs or three lamps with three different color filters. It may thus be considered different from, or a limited special case of, a xe2x80x9cspectrophotometer,xe2x80x9d in that it provides output color information in the trichromatic quantity known as RGB.
Trichromatic quantities may be used for representing color in three coordinate space through some type of transformation. Other RGB conversions to xe2x80x9cdevice independent color spacexe2x80x9d (i.e., RGB converted to conventional L*a*b*) typically use a color conversion transformation equation or a xe2x80x9clookup tablexe2x80x9d system in a known manner. (Examples are provided in references cited herein, and elsewhere.)
A xe2x80x9cdensitometerxe2x80x9d typically has only a single channel, and simply measures the amplitude of light reflectivity from the test surface, such as a developed toner test patch on a photoreceptor, at a selected angle over a range of wavelengths, which may be wide or narrow. A single illumination source, such as an IR LED, a visible LED, or an incandescent lamp, may be used. The output of the densitometer detector is programmed to give the optical density of the sample. A densitometer of this type is basically xe2x80x9ccolor blind.xe2x80x9d For example, a cyan test patch and magenta test patch could have the same optical densities as seen by the densitometer, but, of course, exhibit different colors.
A multiple LED reflectance spectrophotometer, as in the examples of the embodiments herein, may be considered to belong to a special case of spectrophotometers which normally illuminate the target with narrow band or monochromatic light. Others, with wide band illumination sources, can be flashed Xenon lamp spectrophotometers, or incandescent lamp spectrophotometers. A spectrophotometer is normally programmed to give more detailed reflectance values by using more than 3 channel measurements (for example, 10 or more channel measurements), with conversion algorithms. That is in contrast to normal three channel colorimeters, which cannot give accurate, human eye related, reflectance spectra measurements, because they have insufficient measurements for that (only 3 measurements).
The spectrophotometer of the disclosed embodiment is especially suitable for being mounted at one side of the printed sheets output path of a color printer to optically evaluate color imprinted output sheets as they move past the spectrophotometer, variably spaced therefrom, without having to contact the sheets or interfere with the normal movement of the sheets. In particular, it may be used to measure a limited number of color test patch samples printed by the printer on actual printed sheet output of the printer during regular or selected printer operation intervals (between normal printing runs or print jobs). These color test sheet printing intervals may be at regular timed intervals, and/or at each machine xe2x80x9ccycle-up,xe2x80x9d or as otherwise directed by the system software. The spectrophotometer may be mounted at one side of the paper path of the machine, or, if it is desired to use duplex color test sheets, two spectrophotometers may be mounted on opposite sides of the paper path.
Relatively frequent color recalibration of a color printer is highly desirable, since the colors actually printed on the output media (as compared to the colors intended to be printed) can significantly change, or drift out of calibration over time, for various known reasons. For example, changes in the selected or loaded print media, such as differences paper or plastic sheet types, materials, weights, calendaring, coating, etc. Or changes in the printer""s ambient conditions, changes in the image developer materials, aging or wear of printer components, varying interactions of different colors being printed, etc. Printing test color patches on test sheets of the same print media under the same printing conditions during the same relative time periods as the color print job being color-controlled is thus very desirable.
It is thus also advantageous to provide dual-mode color test sheets, in which multiple color patches of different colors are printed on otherwise blank areas of each, or selected, banner, cover, or other inter-document or print job separator sheets. Different sets of colors may be printed on different banner or other test sheets. This dual use of such sheets saves both print paper and printer utilization time, and also provides frequent color recalibration opportunities where the printing system is one in which banner sheets are being printed at frequent intervals anyway.
An additional feature which can be provided is to tailor or set the particular colors or combinations of the test patches on a particular banner or other test sheet to those colors which are about to be printed on the specific document for that banner sheet, i.e., the document pages which are to be printed immediately subsequent to that banner sheet (the print job identified by that banner sheet). This can provide a xe2x80x9creal timexe2x80x9d color correction for the color printer which is tailored to correct printing of the colors of the very next document to be printed.
The preferred implementations of the systems and features disclosed herein may vary depending on the situation. Also, various of the disclosed features or components may be alternatively used for such functions as gray scale balancing, turning on more than one illumination source at once, such as oppositely positioned LEDs, etc.
It will be appreciated that these test patch images and colors may be automatically sent to the printer imager from a stored data file specifically designed for printing the dual mode banner sheet or other color test sheet page, and/or they may be embedded inside the customer job containing the banner page. That is, the latter may be directly electronically associated with the electronic document to be printed, and/or generated or transmitted by the document author or sender. Because the printed test sheet color patches colors and their printing sequence is known (and stored) information, the on-line spectrophotometer measurement data therefrom can be automatically coordinated and compared.
After the spectrophotometer or other color sensor reads the colors of the test patches, the measured color signals may be automatically processed inside the system controller or the printer controller to produce or modify the tone reproduction curve, as explained in the cited references. The color test patches on the next test sheet may then be printed with that new tone reproduction curve. This process may be repeated so as to generate further corrected tone reproduction curves. If the printer""s color image printing components and materials are relatively stable, with only relatively slow long term drift, and there is not a print media or other abrupt change, the tone reproduction curve produced using this closed loop control system will be the correct curve for achieving consistent colors for at least one or even a substantial number of customer print jobs printed thereafter, and only relatively infrequent and few color test sheets, such as the normal banner sheets, need be printed.
However, if there are substantial changes in the print media being used by the printer, or other sudden and major disturbances in the printed colors (which can be detected by the spectrophotometer output in response to the test patches on the next dual mode banner sheet or other color test sheet or even, in certain instances, in the imprinted images) then the subsequent customer print job may have incorrect color reproduction. In these situations of customer print media changes in the printer (or new print jobs or job tickets that specify a change in print media for that print job), where that print media change is such that it may substantially affect the accuracy of the printed colors for that subsequent print job, it is not desirable to continue printing and then have to discard the next subsequent print jobs printed with customer unacceptable colors. In that situation it may be preferable in color critical applications to interrupt the normal printing sequence once the sudden color printing disturbance is detected and to instead print plural additional color test sheets in immediate succession, with different color test patch colors, to sense and converge on a new tone reproduction curve that will achieve consistent color printing for that new print media, and only then to resume the normal printing sequence of customer print jobs. Thus, the subsequent customer print jobs would then use the final, re-stabilized, tone reproduction curve obtained after such a predetermined number of sequential plural color test sheets have been printed.
This patent application is not related to or limited to any particular one of the various possible (see, for example, various of the cited references) algorithms or mathematical techniques for processing the electronic signals from the spectrophotometer to generate or update color correction tables, tone reproduction curves, or other color controls, and hence they need not be further discussed herein.
Various possible color correction systems can employ the output signals of spectrophotometers, using various sophisticated feedback, correction and calibration systems, which need not be discussed in any further detail here, since the general concepts and many specific embodiments are disclosed in many other patents (including those cited herein) and publications. In particular, to electronically analyze and utilize the spectrophotometer or other electronic printed color output information with a feedback analysis system for the color control systems for a printer or other color reproduction system. It is, however, desirable in such systems to be able to use a substantially reduced (smaller) number of color patch samples, printed at intervals during the regular printing operations, to provide relatively substantially continuous updating correction of the printer""s color renditions over a wide or substantially complete color spectra. Noted especially in that regard is the above-cited Xerox Corp. Steven J. Harrington U.S. Pat. No. 6,178,007 B1.
Color correction and/or color control systems should not be confused with color registration systems or sensors. Those systems are for insuring that colors are correctly printed accurately superposed and/or accurately adjacent to one another, such as by providing positional information for shifting the position of respective color images being printed.
Other background patents which have been cited as to color control or correction systems for printers include the following U.S. patents: Xerox Corp. U.S. Pat. No. 5,963,244, issued Oct. 5, 1999 to L. K. Mestha, et al, entitled xe2x80x9cOptimal Reconstruction of Tone Reproduction Curvexe2x80x9d (using a lookup table and densitometer readings of photoreceptor sample color test patches to control various color printer parameters); U.S. Pat. No. 5,581,376, issued December 1996 to Harrington; U.S. Pat. No. 5,528,386, issued Jun. 18, 1996 to Rolleston et al.; U.S. Pat. No. 4,275,413, issued Jun. 23, 1981 to Sakamoto et al.; U.S. Pat. No. 4,500,919, issued Feb. 19, 1985 to Schreiber; U.S. Pat. No. 5,416,613, issued May 16, 1995 to Rolleston et al.; U.S. Pat. No. 5,508,826, filed Apr. 27, 1993 and issued Apr. 16, 1996 to William J. Lloyd et al.; U.S. Pat. No. 5,471,324, issued Nov. 28, 1995 to Rolleston; U.S. Pat. No. 5,491,568, issued Feb. 13, 1996 to Wan; U.S. Pat. No. 5,539,522, issued Jul. 23, 1996 to Yoshida; U.S. Pat. No. 5,483,360, issued Jan. 9, 1996 to Rolleston et al.; U.S. Pat. No. 5,594,557, issued January 1997 to Rolleston et al.; U.S. Pat. No. 2,790,844 issued Apr. 30, 1957 to Neugebauer; U.S. Pat. No. 4,500,919, issued Feb. 19, 1985 to Schreiber U.S. Pat. No. 5,491,568, issued Feb. 13, 1996 to Wan; U.S. Pat. No. 5,481,380 to Bestmann, issued Jan. 2, 1996; U.S. Pat. No. 5,664,072. issued Sep. 2, 1997 to Ueda et al.; U.S. Pat. No. 5,544,258, issued Aug. 6, 1996 to Levien; and U.S. Pat. No. 5,881,209, filed Sep. 13, 1994 and issued Mar. 9, 1999 to Michael Stokes.
A specific feature of the specific embodiment disclosed herein is to provide a color analysis method in which sheets with multiple different color printed test patches are moved relative to a color analyzing spectrophotometer for analysis of respective said color test patches, and wherein fiducial marks are printed adjacent to respective said test patches to be optically detected by a fiducial mark detector to provide a fiducial mark triggering system for providing triggering signals from said fiducial marks for said analysis of said respective test patches, the improvement comprising the automatic diagnostic testing of said fiducial mark triggering system by automatically generating at least one special fiducial mark triggering system test sheet which is read by said fiducial mark detector.
Further specific features disclosed herein, individually or in combination, include those wherein said spectrophotometer is mounted in the paper path of a color printer and said special fiducial mark triggering system test sheet is printed by said color printer and fed through said paper path past said fiducial mark detector and/or wherein more than one said special fiducial mark triggering system test sheet is generated, and wherein at least one said special fiducial mark triggering system test sheet is printed with said test patches of varying density black and/or wherein more than one said special fiducial mark triggering system test sheet is generated, and wherein at least one said test sheet is printed with test patches of varying density black, and wherein then at least one additional said test sheet is printed with variable density black fiducial marks and/or wherein said variable density fiducial marks of said at least one additional said test sheet are printed with variable density data derived from said at least one said test sheet printed with test patches of varying density black and/or a color analysis method in which sheets with multiple different color printed test patches are moved relative to a color analyzing spectrophotometer for analysis of respective said color test patches, and wherein fiducial marks are printed adjacent to respective said test patches to be optically detected by a fiducial mark detector to provide a fiducial mark triggering system for providing triggering signals from said fiducial marks for said analysis of said respective test patches, the improvement comprising the automatic diagnostic testing sequence of said spectrophotometer and said fiducial mark triggering system by automatically generating a sequence of different test sheets of different printed optical densities which are read by said fiducial mark detector and said spectrophotometer and/or wherein said spectrophotometer is mounted in the paper path of a color printer and said sequence of different test sheets is printed by said color printer and fed through said paper path past said spectrophotometer to be read by said spectrophotometer and said fiducial mark detector and/or wherein said sequence of different test sheets includes both minimum and maximum density printed said test sheets and/or wherein at least one said test sheet is printed with different test patches of varying density black and/or wherein at least one said test sheet is printed with a single large test patch of maximum density black and/or wherein said spectrophotometer is mounted in the paper path of a color printer and said sequence of different test sheets is printed by said color printer and fed through said paper path past said spectrophotometer to be read by said spectrophotometer and said fiducial mark detector, and wherein said diagnostic sequence of different test sheets includes a minimum print density full scale output test, a maximum print density minimum scale output test, a patch centering test and a grey scale output test, and fiducial mark detector testing and/or wherein at least one additional diagnostic routine is automatically initiated in response to detecting a failure in said automatic diagnostic testing sequence and/or wherein at least one said test sheet is printed with a single large test patch that is imprinted.
The disclosed system may be connected, operated and controlled by appropriate operation of conventional control systems. It is well known and preferable to program and execute various control functions and logic with software instructions for conventional or general purpose microprocessors, as taught by numerous prior patents and commercial products. Such programming or software may of course vary depending on the particular functions, software type, and microprocessor or other computer system utilized, but will be available to, or readily programmable without undue experimentation from functional descriptions, such as those provided herein, and/or prior knowledge of functions which are conventional, together with general knowledge in the software and computer arts. Alternatively, the disclosed control system or method may be implemented partially or fully in hardware, using standard logic circuits or single chip VLSI designs.
In the description herein, the term xe2x80x9csheetxe2x80x9d refers to a usually flimsy (non-rigid) physical sheet of paper, plastic, or other suitable physical substrate or print media for images, whether precut or web fed. A xe2x80x9ccopy sheetxe2x80x9d may be abbreviated as a xe2x80x9ccopy,xe2x80x9d or called a xe2x80x9chardcopy.xe2x80x9d Printed sheets may be referred to as the xe2x80x9coutput.xe2x80x9d A xe2x80x9cprint jobxe2x80x9d is normally a set of related printed sheets, usually one or more collated copy sets copied from a one or more original document sheets or electronic document page images, from a particular user, or otherwise related.
As to specific components of the subject apparatus, or alternatives therefor, it will be appreciated that, as is normally the case, some such components are known per se in other apparatus or applications which may be additionally or alternatively used herein, including those from art cited herein. All references cited in this specification, and their references, are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features, and/or technical background. What is well known to those skilled in the art need not be described here.